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Canadian  Institute  for  Historical  Microreproductions  /  Institut  Canadian  de  microreproductions  historiq 


ues 


1996 


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1 

2 

3 

1 

2 

3 

4 

5 

6 

MlCtOCOPV    RESOIUTION    TIST   CHABT 

(ANSI  and  ISO  TEST  CHART  No   21 


APPLIED  IIVHGE    I 

1653    Eost    Main    Street 

Rochester,    Ne*   York         14609        uSA 

(7J6)    482  -  OJOO  -  Phone 

(716)    288  -  5989  -  Fa« 


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0/  Wew  ^.^:^'" 


^/ 


^I'V  OP  «««  •S^^ 


.cy 


An  Undescribed  Thermometric  Movement  of  the 
Branches  in  Shrubs  and  Trees '. 


BY 


f 


VV.  F.  G/.NONG,  Ph.D. 

Profator  of  Botany  ir  Smith  Colltge. 

With  six  Figures  in  the  Text. 

O  OME  years  ago  I  noticed  an  apparent  radial  movement  of  the  ascendincr 
^J  branches  in  certain  shrubs  and  small  trees,  whereby  the  branches  were 
brought  closer  to  the  main  stem  in  the  winter,  quite  independently  of  the 
leat-frll,  and  were  separated  from  It  on  the  approach  of  spring.  After  trying 
in  vain  to  find  some  account  of  this  movement,  and  its  causes,  in  the 
literature  accessible  to  me^  and  from  various  persons  informed  on  such 
matters,  I  undertook  a  study  of  it,  with  results  which  follow. 

In  the  autumn  of  .898  I  chose  six  shrubs  and  small  trees,  in  the  Botanic 
Uarden  of  Smith  College,  which  showed  the  movement  and  which  were 
isolated  from  other  woody  plants.  Selecting  long  slender  branches  on  the 
north,  south,  east,  and  west  sides  of  -ach  plant,  I  made  near  the  top  of 
each,  and  on  the  side  radial  to  the  plant,  small  dots  with  water-proof  India 
ink,  the  approximate  positions  of  which  were  marked  for  convenience  by 
coloured  threads.     It  was  then  possible,  with  the  aid  of  an  assistant,  to 

Dec.',^790^^°"""  '^°*'yf°'P''""  Morphology  and  Physiology,  at  its  PhiladclphU  Meeting. 

have'escaLl  IT'  "'' '';''=' /^'■««"'=«'°  '^s  movement,  although  it  seems  unlikely  that  it  coul.l 
have  escaped  not.ce  and  description ;  and  the  cnly  other  mention  of  it  that  I  have  been  able  to  securc 

branches  of  the  Cnkgo  The  inward  movement  of  the  branches  after  removal  of  the  weight  of  the 
^Z'a'  pT"  "  ""  '°  ^  "T"""  1°  nurserymen;  and  some  measurements  of  this  movement  in 
a  shrub  arc  given  m  a  note  by  Agnes  Krye  in  Nature,  vol.  Iv,  1S96,  p.  lyS  and  in  a  bran,.h  „f  h«,  . 
chestnn.  by  Miller  Christy  in  Journal  of  the  Linnean  sJ^uty,  LL'\7,  ".  .oT-l  tZ 
works  of  Wieaier,  Baranetsky,  and  others  on  the  determinant,  of  branch  position  aonearnorto  Jul 
.hi.  subject.  Recently  Mr.  E.  F.  Bigelow,  of  Stamford.  Conn.,  has  writCrthTtl  cordon- 
dent,  of  his  have  asked  him  the  causes  of  branch  movements  noticed  by  them  ;.„  one  caLitTr* 
pruce  whose  branche.  rise  in  wet  weather  and  fall  in  diy.  and  in  the  oth'er  it  w  s  a  pine  wll  d"  d 

lAnnal.  of  Botany,  Vol.  XVm.  No.  LXXn.  October.  1904.J 


6^2     Gattoun^. — Ah   Undescribed  Thertnometric  Movement  of 

measure  with  a  tape  the  distance  between  the  diametrically  opposite  marks 
(i.  e.  from  the  north  to  the  south  branch,  and  from  the  east  to  the  west), 
and  thus  to  determine  any  movement  the  branches  might  make.  The 
method  is  illustrated  by  the  accompanying  diagram  (Fig.  53),  The  resultant 
measurements  for  the  four  shrubs  which  showed  the  most  marked  move- 


FiG.  5a. 


Fig.  53. 


ment  are  plotted   upon  Fig.  54,  and   the  more   important  figures  are 
contained  in  the  following  table: — 


The  riant. 


Salix  laurifolia 
(about  3  meters  high) 


CtrcidifhyUum  jafonicum 
^abuut  2  metets  bigii) 


Comus  florida 
(onder  a  meters  high) 


Brcussonetia  paf^tifeia 
(about  1.5  niclti     !iigh) 


Dale. 


Condition  of  Plant. 


Oct.  10 
Nov.  I  a 
Jan.  ao 
Apr.  a  a 
May  a5 
June  a4 
Oct.  ic 
Oct.  a8 
Jan.  ao 
Apr.  aa 
May  a5 
June  a4 
Oct.  10 
Nov.  I  a 
Jan.  ao 
Apr.  6 
May  35 
June  ;  4 
Oct.  10 
Nov.  la 
Jan.  ao 
Apr.  a  a 
May  aj 


Leaves  all  on 
Leaves  all  gone 
In  full  winter  condition 
Buds  beginning  to  swell 
Leaves  all  out 
In  full  summer  condition 
Leaves  all  on  (nearly) 
Leaves  all  gone 
In  full  winter  condition 
Buds  beginning  to  >well 
Leaves  nearly  all  out 
In  full  summer  condition 
Leaves  all  on 
Leaves  all  gone 
III  full  winter  condition 
Buda  swelling 
Leaves  well  out 
In  full  summer  condit-on 
Leaves  all  on 
Leaves  all  gone 
In  full  winter  condition 
No  trace  of  leaves 
The  plant  evidently  win- 
ter-killed 


N.andS. 


a6i.acm, 

257 
348.5 

245 
ayo.5 

a93 

>'4-.'> 

110.5 

to6 

107 

lla 

118 

'33-3 
114.7 

>09-5 

J'3 

lai 

■36 
1 68.  a 

»5a-4 
'4»S 
«36.5 
lag 


E.  and  W. 


347  cm. 
341.7 
234 
»3» 

367 

274 
ia8 

"5-3 

1315 

laa 
138 

130 

3367 

307.3 

304 

304 

317 

nh 

306.8 
187.8 

"74-5 

'h 
150 


the  Branch'",  in  Shrubs  and  Trees. 


633 


J 


These  measurements  showod  :— 

T.  A  large  inward  movement  accompanyinfj  the  fall  of  the  leaves,  and 
an  outward  movement  accompanyinfi  the  formation  of  new  leaves. 

a.  A  real  seasonal  movement  independent  of  leaf-fall  and  Icaf-fnrma- 
tion.  consisting  in  an  inward  movenent  during  the  advancing  winter,  and 
an  outward  movement  on  the  approach  of  spring. 

3.  Certain  fluctuations  in  the  movements,  the  reasons  for  which  were 
n^i:  evident. 

The  causes  of  the  movement  accompanying  leaf-fall  and  leaf-formation 
arc  so  evident  as  hardly  to  call  for  comment ;  the  movement  is  simply  due 
to  the  removal  of  the  weight  of  the  leaves  and  the!,  contained  water  from 
the  elastic,  obliquely-ascending  branches  in  the  one  case,  and  the  addition 
of  weight  in  the  other.  But  tlu  cause  of  the  further  seasonal  move- 
ment of  the  leafless  branches  is  not  at  once  evident. 

The  measurements  showed  not  only  that  there  is  a  real  movement  of 
the  leafless  branches,  but  that  it  is  of  considerable  amount,  rcachin- 
between  leaf-fall  and  leaf-formation—  '^ 

I  a  cm.,  or  5  %  of  the  total  diameter  of  the  plant  in  Salix  lauri folia  ; 

3"-5  cm.,  or  over  3%  of  the  diameter  of  the  plant  in  Cercidiphyilum 
jafonicum  ; 

5^i  cm.,  or  over  5  y,  of  the  diameter  of  the  plant  in  Cvrnus  Jlon,fa ; 
And  a  larger  though  uncertain  amount  in  Broussonetia  papyrifcra 
The  results  were  of  such  interest  that  a  more  careful  study  of  the 
subject  was  undertaken  the  following  winter  (i 899-1900).  An  improve- 
ment was  made  in  the  method  in  two  respects.  First,  the  movement 
of  each  branch  was  measured  separately  in  order  to  determine  whether 
there  was  any  difleiencc  in  the  movement  of  the  different  branches. 
This  was  effected  by  placing,  in  all  measurements,  the  loop  of  the  tape 

l^.^u*^*'''''"^"  ^*^^^  **P*  **  ""^^  ^^"^  preceding  year)  over  a  brass  screw 
held  by  a  cork  set  in  the  top  of  a  piece  of  stout  gas-pipe,  which  was  driven 
firmly  mto  the  ground  as  nearly  as  possible  in  the  centre  of  the  shrub  (as 
represented  by  Fig.  sz).  It  is  important  to  note  that  this,  like  any  other 
method  of  measuring  such  movements  from  a  fixed  point,  does  not  give 
strictly  accurate  results,  because  the  marks  on  the  branches  do  not  move 
in  and  out  along  the  same  radial  line,  but  in  different  lines.  In  general 
however,  the  errors  from  this  source  are  very  slight,  they  tend  to  neutralize 
one  another,  and  as  ?  .^hole  they  affect  the  results  in  the  direction  of  „ 
lesser  rather  than  a  greater  amount.  Secondly,  some  suggestion  having 
arisen  that  temperature  might  have  an  effect  upon  the  process,  the  air 
temperature  was  recorded  at  each  measurement.  The  measurements  were 
made  by  one  of  my  senior  students,  Miss  Phoebe  Persons,  as  often  as  the 
weather  would  permit,  throughout  the  autumn,  winter,  and  spring.  One  of 
the  greatest  difl^culties  in  this  study  consists  in  the  fact  that  the  measure- 


634     GaitoHs^. — An  UndcHribtd  Tlurmomdrk  Atovimcnt  of 


Fig.  m- 

Abscissa  spaces,  each  two  days. 
Ordinate  spaixs,  each  a-5  mm.  of  movement. 

Downward  direction  me.ins  inward  of  the  shrub,  and  upward  means  outward. 
Showing  the  seasonal  movement  of  four  shrubs  : — 
The  upper  is  Salix  laurifolia, 
the  second  is  CerciJif'hyllum  japonUum, 
tlie  third  is  Contus  JJorida, 
the  lower  is  Droussonctia  papyrifera. 

The  entire  lines  arc  the  north  and  south  measuremcnti 
the  dotted  lines  are  the  east  and  west  measurement, 
the  vertical  lines  across  the  polygons  represent  the  tin- 
first  .nppearance  o.''the  leaves  from  the  !ind  (the  lat 
The  disagreement  of  Broiasonetia  was  connected  with  the  death  (.w.ntcr-ktlling)  of  the  plunt. 


complete  leaf-fall  and  of  the 
r  Comus  was  not  recorded^. 


the  Jiraiu/ics  in  S/inibx  and  Tnrs. 


635 


^WP!t}'!<W""l!' I '  'l""l"i  I'"  I" '""  l"'i[in'|!"i|'>litHH|J4i.'!Ti^ 


,  I     1  u.     I 


.     . 


r  f 

/ 
/ 


'    '    .  N  r    K.  •  /  \     1  N-f't '  ('»t  '  ' 


.    t    .  u 

■f    i     r 


1  tt;j+t  ^t'  - 


j.;r^iiiteni»!.teJ.fl 


uflw- 


i:     : 

.;^... 

Fig.  55. 
Aliscissn  siiaces,  each  two  days. 

Ordinate  spaces,  each  i-i,  ram.  of  movement,  and  I  degree  of  lemperatnre. 
Downward  direction  means  inward  of  the  shrub,  and  upward  means  outward. 

The  plate  shows  the  move.nent  of  the  brunches  in  two  shrubs : 

The  upper  is  LinJera  Htnzoin,  the  north,  south,  east,  and  west  branches  bete         sci  ted  by 

the  initials  N.  S.  E.  \V. 
The  lower  is  Salix  laurifolia,  the  respective  branches  being  indicated  M  f<  r  the  *fro. 

The  double  line  between  the  two  shrubs  represents  tcmpc-atuic 
Tie  records  begin  alter  the  leaves  were  mostly  fallen,  and  continue  until  the  new  le 
largely  formed. 


X  X 


636     CiOHjr.^^n  Undmribed  7ku..omiinc  Afovenunt  of 
ment.  can  be  made,  specially  when  any  of  the  leave,  are  on   onlv  In 
perfectly  .t,  I  weather  ;  and  hence  a  continuou.  .tudy  oJ  the  n.ovement   n 

and  It  was  not  attempted  by  us.  ^' 

♦,Ki  T''?  '''"'il  '*"'''"*'  •^"'''■"»-'  ^'"^  ^'"'"  ^«™  the  seven  IJ.ted  fn  the 
table  bc-Iow.  The  results  of  the  measurement,  of  all  .even  were  exceut  for 
mmor  differences,  very  similar,  and  they  are  fully  illusL^rbv  »S  / 

17Z7ZT''"  7;"?"'^^"'^  °' ''"'  •--■-•  -^  '^"^^  '--'>/-.  wh  h 

to  «!-.„,  -^  r  ""u  ''*  "''"^'^  '^^  ^"''''''  movement  of  them  a!  The 
to  a  amphtude  of  the  movement  between  leaf-fall  and  Icaf-formubn  for 
all  he  branches,  and  the  percentage  which  this  movement  is  ot  1  shrub 
radius,  arc  shown  by  the  following  table  —  "^ 


J'kHt. 


iyrus  americana 

Sa/ij  laiirij'tlia  ,     , 

i  irnits  si'riiea     .... 

6  trcidifhyllum  japoniium 

CornusJIoriJa 

I.intlera  Henzoin 

Ciiifinus  eare/iuianus 


I     Siu  in 
melrtj, 
ht.  diam, 

I-90X  1-10 
'  4-JOX3.IO 
iio  x  1.90 
a-Sox  1-40 
»'.10x  1.90 
i'6o  x  1.30 
a-3ox  a-oo  i 


AUvtmtnt  in  ctHlimttrts. 

Pirttnla^t  movimtnl. 

N. 

S, 

E. 

W. 

A». 

N. 

s. 

E. 

W. 

Av. 

— 

»-3 
il-a 

••4 
6.0 

.V7 
9-4 

'.X 

a-ao 

M.65 

03 
■  a 

Oi 

09 

07 
10 

09 

3-J 
10 

.va 

a  8     3.9 

47 

.V05 
37J 

07 
'3 

05 
oa 

04 

07 

05 
oa 

?.:^ 

5-4 
3  ' 
8.4 

'5      ,<i 

S-9 

«'4S 

o« 

03 

"7 

01 

4-5 

S4      81      4  5 

S-a? 

09 

06 

la 

06 

9-J      8.7     9.J 

9-oa 

II 

or 

07 

07 

N.0 

..  _. 

>07 

.13-a    466 

371 

60 

34 

.M 

34 

«-8     4.7     6.6  j 

5-3 

H 

4.8 

7-7 

4.8 

through  ^,    \    r       ."'"""""  '^"  "^^*=*  °f  fluctuations  of  temperaMre 
through  a  single  day.  and  the  eflfect  of  the  fall  of  temperature  at  niX 
Miss  Persons  made,  after  several  unsuccessful  attempts. 7serLs  of  measure 
ments  through  one  still  day  and  part  of  the  next,  and  f^und   hat  wZ   he" 
mjts  of  a  single  day  and  night  the  movement  was  considerable  and  tha! 

rdT  ttt^' A^'l'^'-P^^^^-^,  ^^-^"-  ^^-S'^  lagginglmewt: 
dir^rt^^V    J  •  ^^  '"'^'  "'^  measurements  made  by  her  was 

directed  to  determine  whether  the  movement  was  most  pronounced  L  Z 

ment  with  any  peculiarities  of  anatomical  structure. 


Iht  nranches  in  Slirubt  and  Tras. 


In  summ.ir>-  the  results  itiowcci  — 

March,  when  an  outwarcl  rovcnlni  C  '""""^  ^'""^  "^*^-^«"  ""'" 

typical  ex  ,  pes  on  , "  l"^.  "'T"t"'  "^'"  »^"'l.cra.ur<.  (as  shown  by  the 
Z  a  lower  „  an  .1 V  i;i  ;  '  '■■  *^'"r' ''""  '''^''^  '"  «"  -"--'•. 
Within  a. single  d^yan^'^Kht     ""'"'"■'"'  ""  ""^^^"'^"^  -l.prcciabij 

agrcLl'rvcrenTi':'  '"''";;";-'-,'"  ^'-  -ovemon.,  and  apparently 
ThccirTorrcir     ',,' ^"^  "■^' "'•»""'-"»•»  an.!    .est  branches. 

of  ten,p:r:;:::  tZ' .  „;  rrii'i^rr^'^^  t^^-^^"  ^'-^  ^"-•^- 

close  enough  to  wirnnt  the  a.    l\  T  •""'  ""i'^rtant,  an.i  it  i, 

««r«.     oincc  me  njiiior  m(»venicnt   s  of  tins  chAnr  ,.r  .1,- 

c.sp„.-.lly  a,  no  precaution,  wcc  t'to    to  ,1"    K       .    '"'"Z  "■"  "'°"-' 
Icng.      nd  di«ancc  from  ,|,e  «nl  il  00^    F    .t  .  ""  "'  ""^  -'""•■ 

did  move  the  mo.t  and  l,.„™   1     ?n  '"'  ""''  ""■"  '"•iKhos 

observed,  it  seemed  o  Jn  ThTt  .1        ,    ^      'r   ^*=^'^^''"S:  the  facts  so  far 
cither  one  of  he!e  £      L     5e  I  "'^'^  ^"°  "'"^'^'"^"^^  -^^^  ^^ 

.econdary  i-war^an^: -2;r.^,::Ls\  l^  Tbe^Xo^^  ^'^^ 

intensifications  and  weakenings  nf  th,.  r    .       /  '  ^^^^^porary 

producing  the  seasonal  ZLentor(7MhtT'1  'T  '^""^'^"^^"^^^ 
causes  (or  at  least  to  a  difference  in  thlmH'^  T^  "  '^"^  '"  ^'^^'^^""' 
causes),  the  secondary  flurtnT        V  "^^  °^  operation  of  the  same 

special  causes  eXro^tfrol"%^"^u''"P°'''^>'  movements  due   to 
rhe  facts  at  our  command  see„,ed  at  first  to  puint  to  the  la,  !r 

X  X  2 


638     Ganong. — An  Undescribed  Tltermotnetric  Movement  of 


probability,  and  in  order  to  obtain  a  definite  basis  for  experiment  we 
assumed  that  the  secondary  fluctuations  were  simply  outward  movements 
from  the  seasonal  position.  As  a  physical  (or  mechanical)  cause  of  this 
outward  movement  under  higher  temperature,  it  seemed  to  us  likely  that 
the  warming  up,  "w-i  consequent  swelling,  of  the  inner  faces  of  the  long 
slender  branches  under  the  influence  of  the  sunlight  on  the  warmer  days 
was  sufficient.  Evidently  this  hypothesis  could  be  submitted  to  experi- 
ment, for  not  only  ought  the  outward  movement  to  be  greater  on  a  sunny 
than  upon  a  cloudy  day  of  approximately  the  same  temperature,  but  the 
movement  in  branches  illuminated  at  the  time  of  measurement  on  their 
inner  faces  should  show  more  movement  than  those  at  that  time  shaded,  or, 
still  better,  than  those  illuminated  upon  their  outer  faces.  Simple  as  such  a 
test  appears  the  weather  never  allowed  us  to  put  it  to  satisfactory  use,  and 
the  season  closed  without  its  accomplishment. 

The  following  winter,  1900-1,  I  was  occupied  with  other  matters  and 
did  nothing  with  this  subject;  but  the  next  year,  1901-2, 1  resumed  the 
study.  Influenced  by  the  theory  above  mentioned, 
I  prepared  to  make  more  exact  measurements  than 
before  of  the  respective  movements  of  the  four 
branches,  for  it  was  evident  the  theory  could  be 
tested  by  observing  whether,  as  it  requires,  the 
greatest  amplitude  of  movement  occurs  in  the  north 
branches,  the  next  greatest  in  that  east  or  west 
branch  which  happened  to  be  illuminated  on  its  inner 
face,  and  the  least  in  the  south  branches.  I  made 
an  improvement  in  Miss  Persons's  method  by  re- 
placing the  single  gas  pipe,  which  would  yield  a  little 
under  tension  when  the  tape  was  drawn  tight,  by 
a  perfectly  firm  tripod,  formed  of  three  gas  pipes 
driven  deeply  into  the  ground,  and  bound  immovably 
at  their  tops  by  twisted  copper  wire  into  which  the 
brass  screw  was  set,  an  arrangement  illustrated 
diagrammatically  in  Fig.  56.  Throughout  the  winter 
very  careful  measurements  were  made  of  six  shrubs, 
including  the  Lindera  and  Cercidiphyllum  used  the  previous  winter,  together 
with  two  species  of  Salix  and  two  species  of  Populus  (young  trees).  The 
results  need  not  here  be  given  in  detail,  since  in  general  they  are  simply 
confirmatory  of  those  earlier  obtained.  As  to  the  two  main  points  at  issue 
they  were  as  follows  : — 

I .  There  was  no  such  regularity  or  order  in  the  amplitudes  of  move- 
ment of  the  respective  branches  as  the  theory  required. 

a.  There  was  no  regular  influence  produced  upon  the  movements  by 
the  presence  or  absence  of  direct  sunlight  upon  the  faces  of  the  branches, 


Fig.  56. 


the  Branches  in  Shrubs  and  Trees. 


639 


/\ 


though  in  some  individual  cases  this  did  appear  to  have  some  slight 
effect. 

It  occurred  to  me  during  the  winter,  especially  when  it  became  plain 
that  the  direct  sunlight  played  little  part,  that  perhaps  the  movement  might 
be  due  to  a  warming,  and  hence  swelling,  of  the  inner  faces  of  all  the 
branches  through  a  general  warming  up  of  the  air  among  the  branches  of 
the  shrub  due  to  the  reflection  of  the  sun's  heat  from  one  branch  to  another. 
To  test  this  I  placed  very  accurate  thermometers,  reading  precisely  alike 
and  graduated  to  tenths  of  a  degree,  both  near  the  centre  of  the  shrub  (but 
in  the  sun),  and  outside  the  shrub  a  few  feet  away.  They  showed  that  the 
temperature  among  the  branches  and  that  outside  the  shrub  were  not 
appreciably  different,  thus  eliminating  another  possible  cause  of  the 
movement. 

The  idea  that  a  direct  action  of  the  sun  upon  the  plant  produced  the 
movement  had  therefore  to  be  abandoned. 

The  following  winter,  1902-3,  I  continued  the  study,  concentrating 
attention  upon  two  plants,  Lindera  Benzoin  and  a  species  of  Salix,  which 
had  shown  themselves  particularly  sensitive  to  temperature  changes.  In- 
cidentally I  re-measured  these  two  shrubs  very  carefully  through  the  winter, 
and  the  results  for  Lindera  are  given  on  Fig.  57,  not  because  they  bring 
out  anything  new,  but  because  they  show  with  particular  clearness  the 
correlation  of  movement  with  temperature.  But  the  principal  work  during 
the  winter  was  experimental,  and  directed  to  discover  the  precise  physical 
basis  of  the  movement.  Its  results  were  as  follows.  Certain  observations 
made  while  measuring  the  shrubs  seemed  to  render  it  probable  that  the 
outward  movement  was  caused  by  the  straightening  of  the  curved  branches 
due  to  the  swelling  of  the  air,  and  perhaps  also  the  water,  in  the  stems 
under  the  influence  of  the  higher  temperature.  A  marked  swelling  of  this 
kind  should  produce  a  straightening  of  the  branch  upon  precisely  the  same 
principle  as  it  straightens  the  bulb  of  a  Richard  thermograph.  This  could 
be  tested  by  bringing  typical  curved  branches  from  the  shrubs  on  very  cold 
days  directly  into  a  warm  greenhouse,  and  comparing  the  distance  between 
the  base  and  tip  before  and  after  the  branch  had  time  to  warm  up.  I  tried 
this  in  a  variety  of  ways,  even  bringing  them  abruptly  from  a  temperature 
much  below  0°  (C.)  directly  into  a  large  case  kept  at  a  temperature  above 
30°.  To  make  the  conditions  as  to  water  supply  as  uniform  as  possible, 
I  plunged  the  branches  at  once  into  water  in  some  cfises  (cutting  them 
under  water  higher  up  the  stem  in  some  instances),  and  immediately  sealed 
the  cut  ends  with  shellac  in  others.  The  results  in  all  cases  were  the  same. 
A  slight  straightening  could  often  be  observed  within  a  few  minutes  under 
the  higher  temperature,  but  this  was  always  lost  within  an  hour  or  there- 
abouts, and  was  then  replaced  by  a  gradually  increasing  curvature.  It 
became  plain,  therefore,  that  while   a   rise  in  temperature  might  cause 


640     Ganong.—An  Undescribed  Thermometric  Movement  of 


Fig.  57. 

Abscissa  sjMces  of  upper  five  polygoni,  each  two  days;  of  lower  six  polygons,  one  half-day 

Ordinate  spaces,  each  2  mm  of  movement  (thus  differing  slightly  from  two  preceding  plates)  and 
1  degree  of  temperature,  and  1%  of  water  (for  lower  polygon). 

Downward  direction  means  inward  of  the  shrub,  and  upward  means  outward. 

The  plate  shows  the  movement  of  the  branches  of  LincUra  Benxoin,  the  north,  south  eait  and 
west  branches  being  indicated  by  the  initials  N.  S.  E.  W. 

The  upper  four  polygons  show  the  movement  through  the  season,  and  the  four  below  them  show 
it  upon  a  larger  lateral  scale  through  the  period  of  greatest  secondary  movement. 

The  double  line  represents  temperature. 

The  lowermost  line  represents  the  percentage  of  water  contained  in  Saiix. 

(On  irregularities  in  this  plate  see  note  on  page  644.) 


the  Branches  in  Shrubs  and  Trees. 


641 


a  slight  straightening  and  hence  outward  movement,  which  might  in  the 
uninjured  plant  remain  constant,  such  a  cause  was  wholly  insufficient  to 
account  for  the  entire  amount  of  movement.  That  the  swelling  of  air  in 
the  stem  did  not  produce  the  result  was  proven  by  forcing  air  powerfully 
into  the  stem  with  a  foot  pump,  a  process  always  without  appreciable 
result. 

Having  thus  to  abandon  this  hypothesis  I  turned  to  another,  more 
than  once  taken  up  and  dropped  in  the  earlier  part  of  the  study,  that  the 
movement  was  in  some  way  connected  with  the  quantity  of  water  present 
in  the  stem.  This  was,  indeed,  very  strongly  indicated  by  two  facts: 
(a)  the  Bt  oussonetia  earlier  referred  to  (p.  634)  showed  a  continuous  in- 
curving  of  its  branches  after  the  plant  was  dead,  which  incur\'ing  was 
apparently  correlated  with  the  drying  out  of  the  branches ;  and  {b)  invariably 
during  the  experiments  a  drying  out  of  any  branch  was  accompanied  by 
an  incurving,  that  is,  by  an  inward  movement.  The  incurved,  or  extreme 
inward  position,  is  evidently  the  natural  position  of  the  dry  tissues,  and  it 
seemed  probable,  therefore,  that  the  outward  movement  might  be  corre- 
lated with,  and  proportional  to,  the  amount  of  water  in  the  stem.  This 
supposition  could  evidently  be  readily  submitted  to  experiment.  Accord- 
ingly on  certain  days  showing  extreme  outward  and  inward  movement,  and 
therefore  of  extreme  high  and  low  temperature,  during  the  winter,  I  cut 
from  each  of  these  shrubs  ten  healthy  branches  each  10  cm.  long,  tied  them 
in  bunches,  and  immediately  weighed  the  latter.  They  were  then  dried  for 
several  months  in  a  dry  room,  and  subsequently  for  some  days  in  a  water 
bath.  They  were  then  again  weighed,  and  the  percentage  of  water  in  the 
original  branches  was  thus  readily  determined.  The  results  were  as 
follows : — 


Dale. 


Jan.  19 

Jan.  32 

Feb.  ao 
Feb.  31 
Feb.  34 

Mar.  13 


Temp. 


-18 

8 

-II 

-»5 

5 

J5 


Plant. 


Lindera 
Salix 

ILindtra 
Salix 
!  Lindera 
Salix 
Lindera 

!  Lindera 
Salix 
i  Lindera 
Salix 


Original 
Weight. 


3-99« 
2-960 
3<5i8 
2613 
4.027 

4-03» 
357* 
3-8S4 
3-830 
2870 


Dry 

Amount 

Percentage 

Weight. 

of  Water. 

of  Water. 

J-S." 

'•4.^9 

36-0 

I-i«72 

1-388 

46.8 

3-281 

'•347 

37-1 

«-.l7« 

1.343 

47-5 

a-4<>5 

i.,s6a 

38-7 

1.490 

1195 

46.4 

2-494 

1538 

381 

3-220 

J-35» 

S.vo 

'•533 

1.361 

47-1 

2.073 

1.748 

45-7 

'•483 

1-387 

48-3 

Comparison  oi  these  figures  with  the  amount  of  movement  at  the 
corresponding  dates  (as  shown  on  Fig.  57)  will  show  at  once  that  in  Salix 
the  agreement  between  amount  of  water  and  amplitude  of  movement  is 
very  close,  a  fact  graphically  illustrated  by  the  polygon  at  the  foot  of 


642     Ganong, — An  Undescribed  Thermometric  Movement  of 

Fig.  57.  In  Under  a,  however,  while  there  is  agreement  in  some  places, 
there  is  a  wide  deviation  in  others,  so  it  becomes  plain  that  either  my 
figures  are  in  error  or  else  this  method  is  worthless.  There  is,  however, 
this  difference  between  the  two  plants,  that  as  the  Under  a  dries  it  loses 
some  of  its  buds  and  bud-scales,  while  the  Salix  does  not,  and  my  method 
of  drying  the  stems  did  not  originally  allow  for  this  possible  source  of  error. 
Despite  the  lack  of  agreement  in  the  Lindera,  however,  I  believe  that  the 
testimony  of  the  Salix,  and  also  that  afforded  by  the  gradually  increasing 
curvature  of  all  branches  as  they  lose  water,  indicates  a  fundamental  fact, 
namely,  that  the  movement  is  connected  with  the  amount  of  water  in  the 
stem,  and  that  this  amount  of  water  is  dependent  upon  temperature. 

This  conclusion  involves  two  further  questions ;  (i)  by  what  mechanical 
method  does  the  increased  amount  of  water  produce  the  movement ;  and 
(3)  by  what  method  does  the  variation  in  temperature  produce  a  variation 
in  the  amount  of  water  ?  We  consider  first  the  former,  for  whicli  there  are 
two  possible  explanations:  (a)  the  weight  of  an  added  quantity  of  the 
water  will  tend  to  depress  the  obliquely-ascending  branches  and  may  thus 
produce  the  outward  movement ;  {b)  the  added  water  may  permit  of  the 
larger  absorption  by  the  various  cells  of  the  younger  branches  and  their 
consequent  swelling,  whereby  the  straightening  of  the  stem  must  result, 
precisely  as  any  flaccid  tissue  straightens  with  more  abundant  water- 
content. 

I  have  carefully  tested  both  of  these  possibilities.  As  to  the  first 
I  have  repeatedly  placed  branches  horizontal,  and  forced  water  into  them 
both  under  an  atmosphere  of  mercury,  and  also  under  the  greater  pressure 
of  the  water  directly  from  a  water  tap.  In  such  cases  the  water  would 
be  forced  out  in  a  few  minutes  from  any  injury  incidentally  or  purposely 
made  near  the  tip  of  the  stem,  showing  that  the  water  penetrated  to  the 
end.  In  such  a  case  a  distinct  depression  of  the  branch  can  usually  be 
measured,  but  it  is  never  of  an  amount  as  great  as  the  natural  amplitude 
of  the  movement  in  the  branch  attached  to  the  plant.  Furthermore,  this 
small  amount  of  movement  occurs  in  the  most  favourable  possible  position 
(horizontal)  of  the  branch,  and  would  be  much  less  when  the  branch  is 
partially  upright  upon  the  tree.  When  the  branches  are  placed  upright, 
and  the  water  is  then  forced  into  them,  there  is  very  little,  if  any,  measurable 
movement.  There  is  yet  another  consideration  which  shows  that  it  cannot 
be  the  weight  of  the  water  which  causes  the  outward  movement,  namely, 
that  in  many  of  the  shrubs  which  showed  marked  movement  of  the  branches 
the  latter  are  nearly  vertical  as  a  whole,  and  hence  the  weight  of  the  water 
cannot  act  to  move  them  outward.  The  weight  of  the  water,  therefore,  may 
aid  the  movement  somewhat,  but  it  cannot  be  the  principal  factor  in 
causing  it. 

We  turn  now  to  the  other  explanation,  that  an  added  supply  of  water 


the  Branches  in  Shrubs  and  Trees. 


643 


permits  a  more  active  absorption  by  the  cells  (osmotic  absorption  bv  the 
hving,  and  imbibition  by  the  walls  of  the  dead,  cells)  and  their  consequent 
svvellmg,  thus  producing  a  straightening  and  therefore  an  outward  movement 
of  the  branch.    The  inward  movement  would  be  caused  by  a  lesser  absorp- 
tion  which  would  permit  the  loss  by  transpiration  to  exceed  absorption 
and  hence  render  the  cells  flaccid,  permitting  the  branch  to  assume  its 
natural  curve.    That  there  is  a  steady  loss  of  water  from  the  twigs  during 
the  winter,  including  even  the  coldest  weather  is,  I  believe,  well  known. 
I  have  myself  noted  that,  on  the  coldest  days  in  the  winter  on  which 
measurements  were  made,  little  ice  crystals  stood  upon  the  lenticels  of  both 
Lindera  and  Salix.    Now  this  steady  loss  of  water  implies  a  steady,  even 
though  small,  absorption  through  the  winter.     It  is  well  known,  however 
that  with  decreasing  temperature  the  power  of  osmotic  absorption  falls 
much  more  rapidly  than  the  rate  of  transpiration  ;  hence  with  a  falling 
temperature  the  loss  of  water  from  the  parenchyma  cells  becomes  in- 
creasingly  great  as  compared  with  the  possibility  of  renewing  the  supply 
osmotically;  the  turgidity  of  the  cells  must  then  decrease,  and  the  same 
effect  will  follow  as  if  the  stem  is  dried  out  by  any  other  method,  namely. 
Its  curvature  is  increased  and  hence  an  inward  movement  results.     The 
lagging  of  the  movement  behind  the  temperature-changes,  earlier  men- 
tioned, is  strongly  in  confirmation  of  this  view.    Unfortunately,  my  attempts 
to   test   this   hypothesis   experimentally   have  given   very   unsatisfactory 
results,  so  that  I  am  unable  to  either  confirm  or  disprove  it,  and  as  further 
experiment  is  not  now  possible  until  another  winter,  I  must  leave  its  com- 
pletion to  a  future  time  or  to  others.     But  I  regard  this  as  by  far  the  most 
probable  explanation  of  the  movement. 

Turning  to  the  question  as  to  how  a  higher  temperature  increases  the 
water-content  of  the  stem,  it  is  obvious  that  this  is  bound  up  with  the  still 
unsolved  problem  of  the  physics  of  sap-ascent.  The  roots  of  these  shrubs 
extend  down  below  the  frost  line  in  the  soil,  so  there  is  no  difficulty  as  to 
the  root  supply. 

The  explanation  here  attributed  to  the  movement  obviously  applies  to 
both  seasonal  and  secondary  uations,  and  would  make  them  the  result 
of  the  same  causes. 

As  to  the  significance  of  the  movement  to  the  plant,  I  think  the 
probabilities  are  that  the  movement  is  a  purely  physical  phenomenon, 
merely  an  incidental  result  of  the  operation  of  a  physical  agency  upon  the 
mechanism  the  plant  happens  to  present,  and  that  it  has  no  ecological 
advantage.  It  must  be  noted,  however,  that  it  still  remains  a  possibility 
that  the  movement  may  be  due  to  a  differential  absorption  of  water,  this 
occurring  more  actively  in  the  cells  on  the  inner  than  on  the  outer  faces  of 
the  branches,  in  which  case  it  might  not  belong  under  incidental  or  physical, 
but  under  irritable  movements,  when  it  would  be  removed  from  the  ther- 


644  GanoKs.—Undeseribed  Thermometric  Movement  of  Brancfies. 

momctric  toward,  the  thermotropfc  category.    If  this  should  prove  lo  be 
true  ,t  W.11  render  it  probable  that  the  movement  has  some  ecological  value 
The  inward  movement  of  the  branches  might  be  supposed  to  be  protective, 
decreasing  slightly  the  leverage  of  winter  winds  upon  thern.  and  as  well  the 

X\  *u     .    "^^  '°"  °^  ****''  ^"*  ^  ''•B''t  «  the  amount  of  movement 
that  the  advantage  can  hardly  be  appreciable. 

Since  it  is  not  the  application  of  heat  directly  which  determines  the 
movement,  but  an  indirect  action  through  water  absorption,  it  might  be 
more  exact  to  speak  of  the  movement  as  an  indirect  thermometric 
movement. 

In  summary: — 

{a)  Some  shrubs  and  small  trees,  and  probably  very  many,  exhibit 
a  marked  mward  and  outward  movement  of  their  naked  winter  branches. 

Kb)  Two  forms  of  the  movement  occur,  a  primary  or  seasonal  move- 
ment, inward  during  the  early  part  of  the  winter  and  outward  in  spring, 
and  a  secondary  movement  which  is  inward  with  a  fall  and  outward  with 
a  rise  of  temperature.  Probably  these  two  are  due  to  the  same  causes,  the 
seasonal  being  simply  a  secondary  movement  of  laige  a.nplitude. 

{c)  The  movement  is  correlated  with  changes  of  temperature,  though 
It  is  not  caused  by  temperature  directly,  but  by  the  larger  or  smaller 
quan  .ties  of  water  which  the  temperature  determines  in  the  plant.  A  smaller 
quantity  of  water,  due  to  transpiration  exceeding  absorption,  decre  ;e. 
turgidity  and  permits  the  natural  inward  spring  of  the  branches  to  manifest 
Itself,  while  a  larger  quantity,  due  to  absorption  exceeding  transpiration, 
permits  an  increase  of  turgidity  and  consequent  swelling,  straightening,  and 
outward  movement  of  the  stem.  &  &  s.      " 

(</)  The  movement  has  probably  no  ecological  significance,  but   is 
thermomrtric"^'  ^^  ^^  construction  of  the  stem,  and  is  properiy  indirectly 


